• Ian Sutton

A Clunky Sentence

Updated: Mar 18


The report Global Warming of 1.5°C report, published in the year 2018 by the IPCC (Intergovernmental Panel on Climate Change), is one of the most important climate change documents ever published, for two reasons. The first reason is that it provides a thorough summary of much of the research that has been carried out on climate change. Hence it has high credibility. The second reason for its importance is that it contains the following memorable sentence.

In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO₂ emissions decline by about 45% from 2010 levels by 2030 (40–60% interquartile range), reaching net zero around 2050 (2045–2055 interquartile range).

Of this statement, the journal Bloomberg Green says,

Like most statements the IPCC sets down, the most important sentence ever written is just terrible—clunky and jargon-filled. What it says, in English, is this: By 2030 the world needs to cut its carbon-dioxide pollution by 45%, and by midcentury reach “net-zero” emissions, meaning that any CO₂ still emitted would have to be drawn down in some way . . .
. . . it may turn out to be the grammatical unit that saved the world. If not, it'll be remembered as the last, best warning we ignored before it was too late.

Because the phrase ‘Net Zero by 2050’ is so pithy and memorable it has been adopted by companies and governments around the world as their mission statement. Yet there is nothing inherently special about the word ‘Zero’ or the year ‘2050’. Climate change is a process — it is not an event that takes place at a singular point in time. But ‘Net Zero by 2050’ is an easy-to-grasp target that can be understood by people who do not know much about climate change.


The danger with catchy slogans is that they can substitute for action. Therefore, it is important to look at how we are actually doing when it comes to actual CO₂ (carbon dioxide) levels.


Human beings have walked this Earth for around 300,000 years. Figure 1 shows that the concentration of CO₂ in the atmosphere has remained well below 300 ppm for most of that time. But then, sometime around the year 1950, CO₂ concentrations took off. We are now at 415 ppm, and there is no end in sight.


Figure 1

Figure 2 is the ‘Keeling Curve’ — the measurement of CO₂ concentration that has been recorded for many decades at the same site in Hawaii. It shows that the concentration of CO₂ in the atmosphere continues its inexorable, upward march. Indeed, it appears as if the rate of increase is itself increasing.

Figure 2

Figure 3 shows annual emissions of CO₂ from human activities since the 19th century. Once more, we see an inexorable rise, starting around the year 1900, but really kicking in by the middle of the 20th century.

Figure 3

The dotted line in Figure 3 shows what we need to do in order to achieve ‘Net Zero by 2050’.


So, we have a great slogan, one that has been adopted by many organizations around the world. In response we see a flurry of activity, such as the rapid adoption of electric vehicles. But the reality is that we have not even started to “bend the curve”.

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